The invention is directed to a power shovel including a dipper for gathering material from a bank and then moving the material to either a material pile or a truck for removing the material from the work site. More particularly, this invention is directed to a mechanism for reducing structural damage to the power shovel boom.
The power shovel includes a platform and an upwardly extending boom pivotally connected at the lower end to the platform. The boom is held in a upwardly and outwardly extending relation to the platform by a brace in the form of tension cables which are anchored to a back stay of a stay structure rigidly mounted on the platform. The power shovel also includes a dipper connected to a dipper handle. The dipper handle is slidably supported in a saddle block which is pivotally mounted on the boom. The dipper handle is movable away from and towards the boom in order to engage the bank of material. In some circumstances, the dipper can engage a hard surface. If the dipper and dipper handle continue to move away from the boom, then the boom will be pivoted away from the dipper. This is not a desirable situation. When an operator detects that this has happened, the operator will pull the dipper back towards the boom. If this occurs too quickly, and it often does, the boom will come down with a impact against the tension cables which support the boom. This situation of causing the boom to be pivoted away from the dipper and then brought back down with an impact on the boom is referred to as boom jacking.
Still more particularly, this invention is directed to a mechanism for automatically setting the boom down softly when boom jacking occurs.
In conventional shovels (See FIG. 2), boom jacking protection is provided by a rod 34 which has a first end attached to the boom 15 and has a second end which extends through an opening into the machinery housing. Included on the rod second end is a limit switch engaging member 31. Mounted adjacent the rod 34 within the machinery housing are a pair of spaced apart limit switches 33 and 35. The first limit switch 33 is intended to be engaged by the limit switch engaging member 31 upon initial pivoting of the boom 15. In order to properly set the location of the first limit switch 33 in order to respond to initial pivoting of the boom 15, the first limit switch 33 is adjustable in its position along the length of the rod 34. When the first limit switch 33 is engaged, a control takes over causing gradual movement of the dipper and dipper handle 25 towards the boom 15. Since in many instances the first limit switch 33 is not in the proper position to accurately reflect a true boom jacking situation, many operators move the first limit switch 33 back to where substantial boom jacking must first occur before the first limit switch 33 is engaged.
The second limit switch 35 is intended to be engaged when substantial boom jacking has occurred. When this happens, the operator brakes are set, and the operator must manually release the brakes before continuing digging operations.
This invention substantially improves over this prior art construction. The location of a first limit switch position is no longer variable. The device of this invention automatically sets a reference set point. As a result, operators can no longer reduce the ability of the system to properly react to a boom jacking situation.
This invention is a shovel including a dipper for gathering material from a bank, a platform, an upwardly extending boom connected at a lower end to the platform, and a sheave rotatably amounted on the upper end of the boom. The shovel further includes a winch drum mounted on the platform, a hoist motor for rotating the winch drum, and a hoist rope extending from the winch drum over the sheave and attached to the dipper. The shovel further includes a saddle block pivotally mounted on the boom, and a dipper handle slidably supported by the saddle block, and pivotable relative to the boom by the saddle block. The shovel further includes dipper handle moving means for moving the dipper and dipper handle away from and towards the boom, the means including a crowd motor, and crowd motor operating means for operating the crowd motor. The shovel further a linear resolver mounted on the platform, a rod having one end pivotally attached to the boom and another end attached to the linear resolver, movement of the rod causing a change in position of the linear resolver, a position means for determining the position of the linear resolver, and means communicating with the position means and the crowd motor control means for moving the dipper handle toward the boom in response to the position means indicating the linear resolver has changed its position from a set point.
In one embodiment, the linear resolver includes a magnet slidably mounted on a base attached to the platform. The shovel further includes a set point determining means for determining the linear resolver set point, the set point determining means including hoist pay out means for determining how much of the hoist rope has been paid out, start means for determining if the power shovel electrical power system has been turned on, and means communicating with the hoist pay out means and the start means for selecting the set point at the position of the linear resolver when the power shovel electric power system is turned on when the hoist pay out means indicates that the hoist rope has been substantially paid out.
One of the principle objects of this invention is to substantially reduce boom damage caused by boom jackings.